What is the product you are trying to use???
cc's and ml's are generally exactly the same measurment. Mg's are something different various solutions have different mg quatities in a given cc or ml. So if this is sustanon 250, then every cc or ml will contain 250mg's of the steroid (sustanon).
If you are referring to test enanthate 250 same thing there is 250mg's of enanthate per cc or ml.